Chapter 28, Problem 44P

Connections to the body for electrocardiography (ECG) and electroencephalography (EEG) are normally made with metal electrodes and conductive gels to ensure good electrical contact. An alternative is the capacitively coupled noncontact electrode, which uses a conductor near but not contacting the skin, to form a capacitor. Clothing can serve as the capacitor’s insulation, eliminating skin contact. A particular EEG instrument calls for capacitive electrodes with maximum reactance 10 MΩ at a typical EEG beta wave frequency of 25 Hz. What’s the minimum electrode capacitance?